A. Nirmala Menon,* K.P.Padmakumari, B.Sankari Kutty, M.A.Sumathikutty, M.M.Sreekumar and C. Arumugham

Abstract: The original aroma compounds responsible for the fresh ginger flavor were isolated by Amberlite XAD-2 chromatography. Ginger oil was isolated by hydrodistillation from fresh ginger. Fresh ginger was dried and the oil was isolated by hydrodistillation from dry ginger (sun-dried and drier-dried). The oils were analyzed by GC and GC/MS. It was found that geranial (24.2%) and zingerone (14.2%) were the major compounds in the original aroma of fresh ginger and their contents decreased during processing. It was observed that the hydrocarbon content of the oil increased and the oxygenated compounds decreased as ginger was processed into dry ginger and ginger oil.

Ginger has been used as a spice for over 2000 years. It is a common additive in many food preparations, and beverages and is valued for its pungency and flavor. It is well accepted that the drying process introduces flavor changes to ginger, but the exact chemical nature of these changes is not clear. Earlier workers (2,3) reported a decrease in the monoterpene and citral contents relative to the sesquiterpene hydrocarbons, presumably due to the difference in the volatility of these of compounds. However, all these studies used steam distillation as the isolation method for volatile compounds, and the severity of the process is itself potentially likely to have introduced changes in the oil produced from the original spice. Effects of drying on Australian grown ginger have been studied by Australian workers (3). The major effects of drying process are found to be a reduction in the gingerol content, an increase in terpene hydrocarbons, and the conversion of some monoterpene alcohols to their corresponding acetates. Another study (4) showed that far infrared drying at 60°C preserved the level of the sesquiterpene hydrocarbons: zingiberene, β-sesquiphellandrene, β-bisabolene and ar-curcumene. Some changes were observed in the levels of the pungent compounds, but the monoterpene levels were not studied. It is well known that monoterpenes and oxygenated compounds are particularly vulnerable to chemical changes under the steam distillation conditions (5). Many reports are available on the chemical composition ginger (6-15). The composition of oil has been studied quite extensively and over 200 volatile compounds have been detected. The importance of isolation conditions is illustrated by attempts to examine the effects (14,15). In the present study, we have studied the chemical changes taking place in the natural aroma compounds of fresh ginger during drying and hydrodistilling.